In general, an organic light emitting phenomenon indicates conversion of electric energy into light energy by means of an organic material. An organic electro-luminescence device using the organic light emitting phenomenon generally has a structure including a cathode, an anode, and an organic material layer interposed therebetween. Herein, in many cases, the organic material layer may have a multi-layered structure having respective different materials in order to improve efficiency and stability of an organic light emitting device. For example, it may include a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and the like.
In the structure of such an organic electro-luminescence device, when a voltage is applied between the two electrodes, holes from the anode and electrons from the cathode are injected into the organic material layer. When the injected holes combine with the injected electrons, excitons are formed. Then, when the excitons return to a ground state, light is generated.
Materials used as an organic material layer in an organic electro-luminescence device may be classified into a light emitting material, a hole injection material, a hole transport material, an electron transport material, an electron injection material, etc. according to their functions.
Further, the light emitting material can be classified into a blue, green or red light emitting material and a yellow or orange light emitting material required for giving a more natural color, according to a light emitting color. Also, a host/dopant system can be used as the light emitting material for the purpose of enhancing the color purity and the light emitting efficiency through energy transfer. It is based on the principle that if a small amount of a dopant having a smaller energy band gap and a higher light emitting efficiency than a host mainly forming a light emitting layer is mixed with the light emitting layer, excitons which are generated in the host are transported to the dopant, thus emitting a light having a high efficiency. Herein, since the wavelength of the host is moved according to the wavelength of the dopant, a light having a desired wavelength can be obtained according the kind of the dopant.
Also, it was reported that as an electron transport material, organic metal complexes from among organic monomolecular materials, which have a high stability against electrons and show a relatively high electron moving speed, are preferable. Especially, Alq3 having a high stability and a high electron affinity was reported to be the most excellent, and is most basically used at present. Also, there are conventionally known electron transport materials such as a flavon derivative (Sanyo), or germanium and silicon cyclopentadiene derivatives (Chisso) (Japanese Patent Publication Nos. 1998-017860, and 1999-087067).
Also, as electron injection/transport materials, organic monomolecular materials having an imidazole group, an oxazole group, and a thiazole group have conventionally frequently been reported. However, before these materials were reported as the electron transport materials, the application of the materials' metal complex compounds to a blue light emitting layer or a blue-green light emitting layer of an organic electro-luminescence device had been already reported.
In order to allow the organic electro-luminescence device to fully exhibit the above-mentioned excellent characteristics, a material constituting the organic material layer in the device, for example, a hole injection material, a hole transport material, a light emitting material, an electron transport material and an electron injection material should be essentially composed of a stable and efficient material. However, the development of a stable and efficient organic material layer material for the organic electro-luminescence device has not yet been fully realized. Accordingly, the development of new materials is continuously desired.